1. Technology Field
The present invention generally relates to optical transmitters. In particular, the present invention relates to an optical device including an optical transmitter, wherein the optical device is capable of dynamically measuring and compensating for the laser slope efficiency of an optical signal produced and transmitted by the optical transmitter.
2. The Related Technology
A properly operating light source is integral to functionality of an optical transmitter. Such light sources, including for example a laser diode positioned in a transmitter optical subassembly of an optical transceiver module, should conform to pre-defined parameters propounded by the manufacturer or applicable industry. These pre-defined parameters involve various characteristics of the optical signal produced by the laser, such as average light level, extinction ratio (“ER”), and optical modulation amplitude (“OMA”). These parameters, which indicate whether the optical signal is adequate for data transmission purposes are defined by the particular physical transmissive interface, i.e., Fibre Channel, gigabit ethernet, Sonet, etc.
Various factors can affect the operating parameters of a laser diode during its optical transmission activities, which can correspondingly cause the laser to exceed acceptable ranges for such parameters. One of these factors is laser temperature. As is known, the ambient temperature in the vicinity of the laser diode within an optical transmitter can fluctuate during operation, thereby affecting the above-referenced parameters. Should one or more parameters exceed predefined acceptable ranges, the optical signal produced by the laser can be adversely affected. Examples of operating parameters for a laser include its average light level, extinction ratio, and optical modulation amplitude.
Known attempts for compensating for laser characteristics dependent upon temperature have involved the use of temperature-sensitive analog components to alert for the need to adjust laser current during operation, which in turn desirably affects laser temperature. In another attempt, laser controllers have been employed that include pre-set laser current or power compensation tables based on digital measurement. In the latter case, detection of an ambient temperature fluctuation can be forwarded to the controller, which consults the pre-set compensation table and instructs the laser controls to be modified accordingly. Such controllers, while partially effective, nonetheless suffer from various disadvantages. Among the disadvantages is the fact that the compensation table used by the controller must be predefined during optical transmitter manufacture, and as such, is not capable of dynamic laser modification according to present operating requirements. Moreover, as each laser is slightly different with respect to other lasers, time must be taken during optical transmitter manufacture to calibrate the laser and the pre-set compensation tables of the controller. This can represent a significant expense in terms of manufacture time.
Another factor affecting laser operation relates to the fact that laser operating properties change over the operational lifetime of the laser. Thus, with all other conditions remaining equal, a laser may still fall outside of acceptable parameter ranges as it advances through its operational lifetime. This operational variability over the life of the laser represents another challenge for maintaining the laser within proper operational parameter ranges.
In light of the above, a need therefore exists for dynamic evaluation of one or more operating parameters of a laser disposed within an optical transmitter, such as a transmitter optical subassembly of an optical transceiver module. Specifically, a need exists for the ability to dynamically measure laser slope efficiency during transmitter operation and to modify the operational characteristics of the laser in order to maintain it within acceptable ranges for specified parameters.